Killing of Bacillus subtilis spores by a modified Fenton reagent containing CuCl2 and ascorbic acid

Multifactorial resistance of Bacillus subtilis spores to low-pressure plasma sterilization

Common sterilization techniques for labile and sensitive materials have far-reaching applications in medical, pharmaceutical, and industrial fields. Heat inactivation, chemical treatment, and radiation are established methods to inactivate microorganisms, but pose a threat to humans and the environment and can damage susceptible materials or products. Recent studies have demonstrated that cold low-pressure plasma (LPP) treatment is an efficient alternative to common sterilization methods, as LPP's levels of radicals, ions, (V)UV-radiation, and exposure to an electromagnetic field can be modulated using different process gases, such as oxygen, nitrogen, argon, or synthetic (ambient) air. To further investigate the effects of LPP, spores of the Gram-positive model organism Bacillus subtilis were tested for their LPP susceptibility including wild-type spores and isogenic spores lacking DNA-repair mechanisms such as non-homologous end-joining (NHEJ) or abasic endonucleases, and protective proteins like α/β-type small acid-soluble spore proteins (SASP), coat proteins, and catalase. These studies aimed to learn how spores resist LPP damage by examining the roles of key spore proteins and DNA-repair mechanisms. As expected, LPP treatment decreased spore survival, and survival after potential DNA damage generated by LPP involved efficient DNA repair following spore germination, spore DNA protection by α/β-type SASP, and catalase breakdown of hydrogen peroxide that can generate oxygen radicals. Depending on the LPP composition and treatment time, LPP treatment offers another method to efficiently inactivate spore-forming bacteria.IMPORTANCESurface-associated contamination by endospore-forming bacteria poses a major challenge in sterilization, since the omnipresence of these highly resistant spores throughout nature makes contamination unavoidable, especially in unprocessed foods. Common bactericidal agents such as heat, UV and γ radiation, and toxic chemicals such as strong oxidizers: (i) are often not sufficient to completely inactivate spores; (ii) can pose risks to the applicant; or (iii) can cause unintended damage to the materials to be sterilized. Cold low-pressure plasma (LPP) has been proposed as an additional method for spore eradication. However, efficient use of LPP in decontamination requires understanding of spores' mechanisms of resistance to and protection against LPP.

Main Groups of Microorganisms of Relevance for Food Safety and Stability

Microbiology is important to food safety, production, processing, preservation, and storage. Microbes such as bacteria, molds, and yeasts are employed for the foods production and food ingredients such as production of wine, beer, bakery, and dairy products. On the other hand, the growth and contamination of spoilage and pathogenic microorganisms is considered as one of the main causes to loss of foodstuff nowadays. Although technology, hygienic strategies, and traceability are important factors to prevent and delay microbial growth and contamination, food remains susceptible to spoilage and activity of pathogen microorganisms. Food loss by either spoilage or contaminated food affects food industry and consumers leading to economic losses and increased hospitalization costs. This chapter focuses on general aspects, characteristics, and importance of main microorganisms (bacteria, yeasts, molds, virus, and parasites) involved in food spoilage or contamination: known and recently discovered species; defects and alterations in foodstuff; most common food associated with each foodborne disease; resistance to thermal processing; occurrence in different countries; outbreaks; and associated symptoms.

Inactivation of Bacillus anthracis spores by single-walled carbon nanotubes coupled with oxidizing antimicrobial chemicals

In this study, we investigated the sporicidal effects of single-walled carbon nanotubes (SWCNTs) and SWCNTs combined with oxidizing antimicrobial chemicals, H₂O₂ and NaOCl, on B. anthracis spores. The results indicated that treatment with SWCNTs alone exhibited little sporicidal effect on B. anthracis spores, while treatment with H₂O₂ or NaOCl alone showed moderate sporicidal effect. The combination treatment with SWCNTs (100 μg/mL) and H₂O₂ (1.5%) or NaOCl (0.25%) exhibited much stronger sporicidal effect on the spores, compared to treatment with H₂O₂ or NaOCl alone at the same concentrations, doubling the log reduction of viable spore number (∼3.3 log vs ∼1.6 log). Such enhanced sporicidal efficiency was due to the synergistic effect contributed by the two individual antimicrobial mechanisms of SWCNTs and the oxidizing antimicrobial chemicals. The ordered sequential treatment with SWCNTs and H₂O₂ or NaOCl revealed that SWCNTs played the key role in making the spores more permeable/susceptible to chemicals. This study demonstrated the potential of combination treatment with SWCNTs and oxidizing antimicrobial agents in developing highly effective sporicidal agents/methods.

Detection of protein S-nitrosylation with the biotin-switch technique

Protein S-nitrosylation, the posttranslational modification of cysteine thiols to form S-nitrosothiols, is a principle mechanism of nitric oxide-based signaling. Studies have demonstrated myriad roles for S-nitrosylation in organisms from bacteria to humans, and recent efforts have greatly advanced our scientific understanding of how this redox-based modification is dynamically regulated during physiological and pathophysiological conditions. The focus of this review is the biotin-switch technique (BST), which has become a mainstay assay for detecting S-nitrosylated proteins in complex biological systems. Potential pitfalls and modern adaptations of the BST are discussed, as are future directions for this assay in the burgeoning field of protein S-nitrosylation.

Spores of Bacillus subtilis: their resistance to and killing by radiation, heat and chemicals

A number of mechanisms are responsible for the resistance of spores of Bacillus species to heat, radiation and chemicals and for spore killing by these agents. Spore resistance to wet heat is determined largely by the water content of spore core, which is much lower than that in the growing cell protoplast. A lower core water content generally gives more wet heat-resistant spores. The level and type of spore core mineral ions and the intrinsic stability of total spore proteins also play a role in spore wet heat resistance, and the saturation of spore DNA with alpha/beta-type small, acid-soluble spore proteins (SASP) protects DNA against wet heat damage. However, how wet heat kills spores is not clear, although it is not through DNA damage. The alpha/beta-type SASP are also important in spore resistance to dry heat, as is DNA repair in spore outgrowth, as Bacillus subtilis spores are killed by dry heat via DNA damage. Both UV and gamma-radiation also kill spores via DNA damage. The mechanism of spore resistance to gamma-radiation is not well understood, although the alpha/beta-type SASP are not involved. In contrast, spore UV resistance is due largely to an alteration in spore DNA photochemistry caused by the binding of alpha/beta-type SASP to the DNA, and to a lesser extent to the photosensitizing action of the spore core's large pool of dipicolinic acid. UV irradiation of spores at 254 nm does not generate the cyclobutane dimers (CPDs) and (6-4)-photoproducts (64PPs) formed between adjacent pyrimidines in growing cells, but rather a thymidyl-thymidine adduct termed spore photoproduct (SP). While SP is formed in spores with approximately the same quantum efficiency as that for generation of CPDs and 64PPs in growing cells, SP is repaired rapidly and efficiently in spore outgrowth by a number of repair systems, at least one of which is specific for SP. Some chemicals (e.g. nitrous acid, formaldehyde) again kill spores by DNA damage, while others, in particular oxidizing agents, appear to damage the spore's inner membrane so that this membrane ruptures upon spore germination and outgrowth. There are also other agents such as glutaraldehyde for which the mechanism of spore killing is unclear. Factors important in spore chemical resistance vary with the chemical, but include: (i) the spore coat proteins that likely react with and detoxify chemical agents; (ii) the relative impermeability of the spore's inner membrane that restricts access of exogenous chemicals to the spore core; (iii) the protection of spore DNA by its saturation with alpha/beta-type SASP; and (iv) DNA repair for agents that kill spores via DNA damage. Given the importance of the killing of spores of Bacillus species in the food and medical products industry, a deeper understanding of the mechanisms of spore resistance and killing may lead to improved methods for spore destruction.

Mechanisms of killing of spores of Bacillus subtilis by dimethyldioxirane

AIMS

To determine the mechanisms of Bacillus subtilis spore resistance to and killing by a novel sporicide, dimethyldioxirane (DMDO) that was generated in situ from acetone and potassium peroxymonosulfate at neutral pH.

METHODS AND RESULTS

Spores of B. subtilis were effectively killed by DMDO. Rates of killing by DMDO of spores lacking most DNA protective alpha/beta-type small, acid-soluble spore proteins (alpha- beta- spores) or the major DNA repair protein, RecA, were very similar to that of wild-type spore killing. Survivors of wild-type and alpha- beta- spores treated with DMDO also exhibited no increase in mutations. Spores lacking much coat protein due either to mutation or chemical decoating were much more sensitive to DMDO than were wild-type spores, but were more resistant than growing cells. Wild-type spores killed with this reagent retained their large pool of dipicolinic acid (DPA), and the survivors of spores treated with DMDO were sensitized to wet heat. The DMDO-killed spores germinated with nutrients, albeit more slowly than untreated spores, but germinated faster than untreated spores with dodecylamine. The killed spores were also germinated by very high pressures and by lysozyme treatment in hypertonic medium, but many of these spores lysed shortly after their germination, and none of these treatments were able to revive the DMDO-killed spores.

CONCLUSIONS

DMDO is an effective reagent for killing B. subtilis spores. The spore coat is a major factor in spore resistance to DMDO, which does not kill spores by DNA damage or by inactivating some component needed for spore germination. Rather, this reagent appears to kill spores by damaging the spore's inner membrane in some fashion.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work demonstrates that DMDO is an effective decontaminant for spores of Bacillus species that can work under mild conditions, and the killed spores cannot be revived. Evidence has also been obtained on the mechanisms of spore resistance to and killing by this reagent.

Photodynamic inactivation of Bacillus spores, mediated by phenothiazinium dyes

Spore formation is a sophisticated mechanism by which some bacteria survive conditions of stress and starvation by producing a multilayered protective capsule enclosing their condensed DNA. Spores are highly resistant to damage by heat, radiation, and commonly employed antibacterial agents. Previously, spores have also been shown to be resistant to photodynamic inactivation using dyes and light that easily destroy the corresponding vegetative bacteria. We have discovered that Bacillus spores are susceptible to photoinactivation by phenothiazinium dyes and low doses of red light. Dimethylmethylene blue, methylene blue, new methylene blue, and toluidine blue O are all effective, while alternative photosensitizers such as Rose Bengal, polylysine chlorin(e6) conjugate, a tricationic porphyrin, and a benzoporphyrin derivative, which easily kill vegetative cells, are ineffective. Spores of Bacillus cereus and B. thuringiensis are most susceptible, B. subtilis and B. atrophaeus are also killed, and B. megaterium is resistant. Photoinactivation is most effective when excess dye is washed from the spores, showing that the dye binds to the spores and that excess dye in solution can quench light delivery. The relatively mild conditions needed for spore killing could have applications for treating wounds contaminated by anthrax spores, for which conventional sporicides would have unacceptable tissue toxicity.